Snap-action switch for a thermal trigger, especially for a motor protection device

ABSTRACT

A snap-action switch for a thermal trigger, especially for a motor protection device, having rest contacts, part of which are stationary and another part of which are mounted at an elastic spring actuated by a bimetallic element for opening the contacts. A stop is movable into the path of the elastic spring in front of its dead-center position. The elastic spring possesses a substantially E-shape and is fixedly held at the ends of both of its outer legs between two stationarily mounted support or bearing plates. The support plate which is closer to at least one stationary contact extends along both of the outer spring legs, closer to at least one contact which is mounted at the elastic spring than the other support plate. The central spring leg is moved with its free end by the bimetallic element past the support plates and the stop is movable into the path of a spring web of the elastic spring and such web is enlarged at its side facing away from the spring legs and carries the aforesaid at least one contact.

United States Patent [1 1 Hufschmid l l SNAP-ACTION SWITCH FOR A THERMAL TRIGGER, ESPECIALLY FOR A MOTOR PROTECTION DEVICE [75] Inventor: Max Hufschmid,Niedererlinsbach,

Switzerland [73] Assignee: Sprecher & Schuh AG, Aarau,

Switzerland [22] Filed: Aug. 29, 1973 21 Appl. No.: 392,784

[30] Foreign Application Priority Data Sept. 26, 1972 Switzerland 14021/72 52 us. Cl. 337/365, 200/67 DA 51 Int. Cl. HOlh 37/54 [58] Field of Search 200/67 DA, 67 B; 337/364, 337/365, 390, 343

[ 1 Mar. 18, 1975 Primary Examiner-David Smith, Jr.

[57] ABSTRACT A snap-action switch for a thermal trigger, especially for a motor protection device, having rest contacts, part of which are stationary and another part of which are mounted at an elastic spring actuated by a bimetallic element for opening the contacts. A stop is movable into the path of the elastic spring in front of its dead-center position. The elastic spring possesses a substantially E-shape and is fixedly held at the ends of both of its outer legs between two stationarily mounted support or bearing plates. The support plate which is closer to at least one stationary contact extends along both of the outer spring legs, closer to at least one contact which is mounted at the elastic spring than the other support plate. The central spring leg is moved with its free end by the bimetallic element past the support plates and the stop is movable into the path of a spring web of the elastic spring and such web-is enlarged at its side facing away from the spring legs and carries the aforesaid at least one contact.

1 Claim, 3 Drawing Figures BACKGROUND OF THE INVENTION .arily arranged and partially mounted at an elastic spring actuated by a bimetallic element for opening the contacts. there also being provided a movable stop which can be displayed into the path of the elastic spring in front of its dead-center position.

With most prior art constructions of jump or snapaction switches, which in construction are quite complicated as a general rule, it is not readily possiible to prevent a gradual reduction in the contact pressure prior to separation of the contacts, if there is to be realized an automatic closing of the contacts after cooling of the actuating bimetallic element. With certain stateof-the-art switches, the stationary contacts are resiliently mounted. This additional resilient mounting naturally has a flatter force-displacement characteristic. Furthermore, the stationary contact also shifts or displaces somewhat, which then is absent at the contact spacing during automatic resetting. The consequences of creeping ofthe contacts which arises with the known switches are well known in this particular technology and feared, so that they need not be considered in detail.

The aforementioned drawbacks of contact creeping,

. SUMMARY OF THE INVENTION Hence, it is a primary object of the present invention to provide an improved construction of snap-action switch for a thermal trigger, especially for a motor protective device, which is not associated with the aforementioned drawbacks and limitations of the prior art,

constructions. 7

Another and more specific object of the present invention relates to the provision of a new and improved construction of snap-action switch of the previously mentioned type which effectively avoids creeping of the contacts both during automatic as well as also during manual resetting and possesses a steep contact pressure-displacement diagram upon opening the contacts.

Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the invention provides a snap-action switch of the previously mentioned type which is manifested by the features that a substantially E- shaped spring is fixedly held at the ends of both of its outer legs, which approach one another in the plane of the spring for their pre-bias as the elastic spring, between two stationarily mounted support or bearing plates. The support plate closer to at least one stationary contact extends along both outer spring legs into a position closer to at least one contact mounted at the elastic spring than the other support plate. The central spring leg of the E-shaped spring is movable with its free end past the support plates by the bimetallic element, and the stop is movable into the path of the spring web carrying at least one contact and which is,

enlarged at the side facing away from the spring legs.

This asymmetrical mounting or support of the elastic spring surprisingly brings about such a favorable influencing of the characteristic spring force-displacement diagram at the region of contact of the contacts, that upon separation of the contacts there occurs a jumplike transition. Furthermore, there is favorably influenced the spring characteristics as concerns the deadcenter position of the spring, with the result that the spring component supporting the at least one spring contact again approaches in a jump-like or snap-action fashion the stationary contact during the automatic resetting operation.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:

FIG. 1 is an end view of the switch components without the housing of the snap-action switch of this development;

FIG. 2 is a view of the switch looking in the direction of the arrow II of FIG. 1, however without the stationary contact; and

FIG. 3 is a view of the switch looking in the direction of the arrow III of FIG. 1, again without the stationary contact.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawing, a spring or spring .blade 10 with its contact 10' is stamped from a spring I to be so much shorter than both of the outer longer legs 12 and 13 that it can move past the support or bearing plates 21 and 22 of a support or bearing means 20 stationarily mounted in a housing (not shown), when such actuation leg is moved during the release action by the plunger 30 of a non-illustrated bimetallic element, in FIG. 1 from the left towards the right, or returned back into the starting position. In the case ofa thermal motor protection switch the plunger 30 is actuated by the bimetallic element which is directly or indirectly heated by the motor current. The ends 120 and 13a of the legs 12 and 13 respectively are clamped between the support or bearing plates 21 and 22 in such a manner that they can be retained in close proximity to one another in a pre-biased or stressed state transverse to the plane containing the spring or spring plate 10 by the rivet bolts 4. Consequently, there is provided the spring characteristics of the spring plate 10 which allows such 7 to be suddenly raised in a jump-like fashion from the Now when the stop or impact member 6 is in its fullline position depicted in FIGS. 1 and 2, then the spring plate snaps or whips through into the left-hand position shown in broken lines in FIG. 1, where it then also remains when the plunger 30 (after cooling of the bimetallic element) again moves back towards the left. Then it is necessary to bring the contact back into the full-line right-hand closed position, shown in FIG. I, when the motor again should start-up, by manually actuating the spring plate 10, for instance by means of a switch means (not shown), for instance a suitable pushbutton or equivalent.

However, if it is desired that the motor should again automatically start-up, following adequate cooling of the bimetallic element, then the stop or impact member 6 is placed into the phantom lineposition of FIGS. 1 to 3 by any suitable means, for instance, a push button, slide and so forth. Now if the plunger 30, in the presence of an excess current, is moved by the bimetallic element from the left towards the right, then the web '10" of the spring or spring plate 10 can only snap or shift up to the region of the stop or impact member 6 and into the phantom line or chain-dot line position of the spring plate 10 as shown in FIG. 1, and which position is located to the right of the dead-center position of the spring plate. Hence, upon return of the plunger 30 towards the left, when the bimetallic elements has again sufficiently'cooled, the spring plate 10 automatically again snaps towards the right into the full-line contact position.

With the conventional elastic springs, upon interruption of the contact, there occurs a slow reduction in pressure and a creeping of the contacts. Due to the dissimilarities of the support or bearing plates 21 and 22 such is here avoided in that the support plate 21, situated closer to the fixed or stationary contact 5, extends along the lateral spring legs 12 and 13 closer to the stationary contact 5 than the correspondingly narrower constructed support plate 22. This now causes the spring or spring plate 10, in the left-hand position shown in broken lines in FIG. 1, to further bend-out because there is available for this purpose for the spring a longer length of the legs 12, 13 up to the lower edge 22' of 'the support plate '22 than during bending towards the right into the full-line position of FIG. 1, where it impacts sooner against the lower edge 21 of the support or bearing plate 21. This also requires a displacement of the dead-center position of the elastic spring and improves the contact pressure characteristics, and specifically both directly prior to separation of and also directly during closing of the contacts 5 and 10. Hence, an insufficient contact pressure cannot occur during any switching phase or mode.

Of course, as part of the complete switch, there are also provided the connection tabs and connection terminals, which here have only been conveniently depicted by the tab portions 10' and 5. Furthermore, in order to improve clarity in illustration, the remaining components of the switch, such as the housing, resetting elements and so forth, have been conveniently omitted, particularly since the constructionof such components can be carried out in conventional manner and details of these components are not necessary to the understanding of the basic concepts of the invention.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

l. A snap-action switch for a thermal trigger mechanism, especially for a motor protection device, comprising rest contacts, an elastic spring, which can be actuated by a bimetallic element for opening the contacts, at least one ofv the rest contacts being stationarily arranged and at least one being mounted at the elastic spring, a stop movable into the path of the elastic spring in front of its dead-center position, the improvement wherein said elastic spring comprises a substantially E-shaped spring member having a pair of I outer legs and a central leg, twostationarily mounted support plates for fixedly retaining the E-shaped spring member at the ends of both of its outer legs, means for pre-biasing said outer legs towards one another substantially in the plane of the spring member, one of the support plates which is closer to said at least one stationary contact being constructed to extend along both of the'outer spring legs to a position which is closer to said at least one contact.mounted at the elastic spring member than is the other supportplate, said central leg having a free end and moving with said free end past the support plates under the action of the bimetallic element, said spring member having a spring web carrying said at least one contact mounted thereat and said spring web being enlarged in size at the side facing path of said spring web. 

1. A snap-action switch for a thermal trigger mechanism, especially for a motor protection device, comprising rest contacts, an elastic spring, which can be actuated by a bimetallic element for opening the contacts, at least one of the rest contacts being stationarily arranged and at leAst one being mounted at the elastic spring, a stop movable into the path of the elastic spring in front of its dead-center position, the improvement wherein said elastic spring comprises a substantially E-shaped spring member having a pair of outer legs and a central leg, two stationarily mounted support plates for fixedly retaining the E-shaped spring member at the ends of both of its outer legs, means for pre-biasing said outer legs towards one another substantially in the plane of the spring member, one of the support plates which is closer to said at least one stationary contact being constructed to extend along both of the outer spring legs to a position which is closer to said at least one contact mounted at the elastic spring member than is the other support plate, said central leg having a free end and moving with said free end past the support plates under the action of the bimetallic element, said spring member having a spring web carrying said at least one contact mounted thereat and said spring web being enlarged in size at the side facing away from said legs, said stop being movable into the path of said spring web. 